Cyanine dyes derived from thienylbenzoxazoles and silver halide emulsions sensitized therewith



United States Patent O CYANINE DYES DERIVED FROM THIENYLBENZ- OXAZOLES AND SILVER HALIDE EMULSIONS SENSITIZED THEREWITH Johannes Giitze, Koln-Stammheim, Germany, assignor to Agfa Aktiengesellschaft, Leverkusen, Germany, a corporation of Germany No Drawing. Filed July 29, 1958, Ser. No. 751,621

Claim priority, application Germany Aug. 16, 1957 Claims. (Cl. 96-105) The present invention relates to new cyanine dyestufis and to silver 'halide emulsions sensitized therewith.

For sensitizing silver halide emulsions, especially in the orthochromatic range, it is already known to use cyanine dyes which are derived from Z-methyl benzoxazole or from substituted Z-methyl benzoxazoles. For example, sensitizing dyes which are derived from Z-methyl naphthoxazole have already been mentioned in German patent specification No. 724,608. Alkyl-substituted and hydroxyalkyl-substituted benzoxazole dyes are known from German patent specification Nos. 654,913 and 709,555 and dyes from 2-methyl-5-isoamylbenzoxazole are known firom German patent specification No. 709,873. Those dyes which are derived from. Z-methyI-S-phenyl benzoxazole and which are described in German patent specifications 714,764 and 936,644 have acquired particular significance. They are characterized by a particularly powerful sensitizing action, which is shown in a high sensitivity, for example in the yellow-green range of the spectrum, and in a steep fall in the sensitization curve towards the long-wave range.

It has now been found that cyanine dyes, especially acid cyanines, basic cyanines and neutrocyanines which are derived from 2methyl-5-(wthienyl)-benzoxazole show the same powerful sensitizing action as the phenylsubstituted dyes, which in certain cases is even intensified, and that these dyes absorb about 10 m further into the long wave range, so that also their sensitization maximum is displaced towards the longwave range as compared with the phenyl-substituted dyes. In this way, it is possible to sensitize spectral regions which it has not so far been possible to sensitize with such intensity. The new dyestufiis can be represented by the following gen eral formulae:

wherein:

R represents an organic radical usual in cyanine dye chemistry such as an alkyl, aralkyl, carboxylalkyl or sulphoalkyl radical,

R, R" and R' each represent a hydrogen atom or a substituent usual in cyanine dye chemistry such as an alkyl, aryl, aralkyl, heterocyclic or hydroxyalkyl radical;

A represents a S-a-thienyl benzoxazole radical or another heterocyclic ring system usual in cyanine chemistry, such as substituted or unsubstituted benzthiazole, naphthiazole, thiazole, benzselenazole, selenazole, benzoxazole, naphthoxazole, quinoline ring system,

Q represents the atoms needed for completing a hetero- 3,044,875 Parented July 17, 1962 cyclic ketomethylene ring, which in its turn can be linked by way of a methine group to a 5-a-thienyl benzoxazole ring or to another heterocyclic radical usual in cyanine dye chemistry, and n and m each represent 0, 1 or 2.

The dyes are produced by condensation of the quaternary salts of 2-methyl-5-(a-thienyl)-benzoxazole with intermediate products usual in cyanine dye chemistry and according to known processes, as will be more fully explained in the following examples.

The 2-methyl-5-(a-thienyl)-benzoxazole (VI) serving as starting material has not yet been described in the literature. It can be obtained by the method indicated in the following reaction scheme:

The p-nitrophenyl thiophene (I) serving as starting material has already been described in Journ. Amer. Chem. Soc., vol. 46, page 2343. The reduction to the p-aminophenyl thiophene (II) takes place in the following way:

30 g. of the nitro compound I are stirred to form a paste with approximately cc. of methanol or acetone. This mixture is added in portions to a hot solution of g. of stannous chloride in 120 cc. of concentrated hydrochloric acid. When the addition is complete, the mixture is left to stand for 15 minutes on a steam bath, whereupon it is cooled and the precipitated tin double salt is filtered oif with suction, washed with water and dried. Said salt is decomposed by means of aqueous NaOH solution to obtain the free base which is filtered with suction, water-washed, and dried. For purification purposes, the crude amine recovered from the precipitate can be distilled with steam. The pure base melts at 72 C. and its acetyl derivative has a melting point of 189 C. For conversion into the p-hydroxyphenyl thiophene (III), the base is diazotised at 40 C. in substantially40% sulphuric acid by addition of sodium nitrite and the diazo solution obtained is introduced into boiling copper sulphate solution, the phenol separating out after boiling for a short time. For purification purposes, it is dissolved in an alkali metal hydroxide solution, re-precipitated with acid and extracted with ether. The ether extract is recrystallised from ligroin. The phenol (III) melts at C.

To produce the azo dye (IV), the phenol (III) is dissolved in dilute sodium hydroxide solution, and the equivalent quantity of diazotized aniline is run at 5-10 0. into this solution. The azo dye separating out is filtered off withsuction, washed with water and immediately further processed.

The azo dye (IV) obtained for example from 17 g.

of p hydroxy phenyl thiophene (III) is heated slightly with 150 cc. of ethanol and 20 cc. of sodium hydroxide solution and the mixture is introduced into a hot solution of 150 g. of sodium hydrosulphite, 300 cc. of water and 80 cc. of sodium hydroxide solution. After the solution has become decolorized, another 300 cc. of water are added, the solution is allowed to cool and it is then brought to a pH value of approximately 5 and the hydroxy-amino-phenyl thiophene (V) is filtered oiI with suction.

To produce the new thienyl benzoxazole (VI), 20 g. of the hydroxy amine are boiled for several hours with 150 cc. of acetic anhydride. The anhydride is then distilled oil and the residue distilled in vacuo. During a first distillation, a fraction boiling at 130-210 C. at a pressure of 1 mm. is collected; this product is re-distilled at 0.5 mm., whereupon the desired base (VI) distils over at 140-152 C. and solidifies in the receiver. After being recrystallized from methanol, the Z-methyl-S-(athienyl)-benzoxazole has a melting point of 75 C. Analysis produced the following results:

The calculated values for a compound C H ONS (VI) were:

C, 66.9%; H, 4.2%; O, 7.4%; N, 6.5%; S, 14.9%

The values found were:

C, 66.8%; H, 4.3%; O, 7.7%; N, 6.9%; S, 14.9%

O S CCH so o nt l I/ l VII VIII

The quaternary salts are distinguished by high reactivity and may be transformed by methods known as such into cyanine dyes. By Way of example there are cited the following methods:

Asymmetrical 2,2 -monomethinecyanines (pseudocyanines) are obtained by condensing the above quarternary salts with quaternary salts of heteroeyclic nitrogen compounds which contain an alkyl mercapto, preferably a methyl mercapto group in the alpha or gamma position, suitable heteroeyclic nitrogen compounds being for instance substituted or unsubstituted, benzthiazoles, naphthiazoles, tbiaz oles, benzselenazoles, selenazoles, benzoxazoles, naphthoxazoles, quinolines. In addition to the alkylmercapto group the compounds may have as substituent groups one or more of the following: alkoxy, halogen, alkyl, aryl, ara-lkyl, amino or substituted amino.

4- The dyes derived from alpha alkyl mercapto compounds,

correspond to the general formula:

s N U i t wherein R and R stand for a substituted or unsubstituted alkyl group such as methyl, ethyl, propyl, butyl,

Symmetrical monomethinecyanines are obtained by condensing the above quaternary salts by means of amylnitrite in glacial acetic acid.

Symmetrical carbocyanines are produced by condensing the quaternary salts by ethyl orthoformate in pyridine solution. For obtaining asymmetrical carbocyanines that are unsubstituted in the trimethine chain the quaternary salts are condensed with quaternary salts of heteroeyclic nitrogen bases of the aforementioned type which are substituted in alpha-position by an acylarylaminovinyl group such as an acetylphenylaminovinyl group. Symmetrical carbocyanines which are substituted at the middle carbon atom of the trimethine chain by an alkyl group are obtained by condensing the quaternary thienyl bases with an ortho ester of acetic acid or of a higher fatty acid such as ethyl orthoacetate in pyridine solution. By condensing the above quaternary salts with quaternary salts of heteroeyclic nitrogen bases which contain in alpha-position the group GH:.S'C=CH Alkyl Asymmetrical carbocyanines are obtained which are substituted in trimethine chain by an alkyl group.

Symmetrical pentamethine-, heptamethineand nonamethinecyanines may also be obtained from the quarternary thienyl bases by known methods such as by condensing said bases with aniline acroleine anil or gutaconic aldehyde dianilide in alcoholic solution with sodium ethoxide.

Merocyanines may be obtained by condensing the quaternary salts of the above thienylbenzthiazoles with compounds of the formula:

wherein R stands for alkyl, such as methyl, ethyl, propyl, R stands for an alkoxy or an anilino group and Y stands for oxygen or sulfur.

These merocyanines correspond to the general formula:

wherein R, R and Y have the same meaning as in the preceding formulae.

These merocyanines can be quaternized by known quaternizing agents such as dimethylsulfate, ethyl paratoluene-sulphonate, and the quaternary salts may be reacted with heterocyclic nitrogen compounds having an active methyl group in alphaposition to produce rhodacyanines of the following general formula:

wherein R, R, R A and X- have the same meaning as in the preceding formula.

It is furthermore possible :to condense any other known quaternary merocyanine salts such as those of the formula are Obtained.

VIII.

Another type of dyestufis which may be obtained from In the absorption, the new dyes are clearly displaced further towards the red than the corresponding known phenyl-substituted dyes and they have a much more intense color than the unsubstituted dyes. v The new sensitizers are suitable for blaek-and-white and for color silver halide emulsion and are added to said emulsions in amounts of about 0.005 to 0.05 g. per kg. of emulsion.

The dyes according to the invention do not show any tendency to fogging. The photographic silver halide layers sensitized therewith are stable to storage and do not show any decrease in sensitivity when kept in a heating chamber.

The process will now be explained by reference to the following examples.

6 Example I o\ /0 S CGH=CH-CH=C (T s I l r r I l ((JHM ll zh s03- S0311 5 g. of Z-methyl-S-thienyl benzoxazole and 3 g. of butanesultone are heated for minutes at 140 C. The reaction product is Worked up with acetone and is a yellow water-soluble powder. 4 g. of this powder are heated with 5 cc. of pyridine, 4 cc. of orthoformic acid ethyl ester and 0.5 cc. of acetic anhydride for one hour at -l20 C. The mixture is allowed to cool, the greasy dye is dissolved in methanol and the dye is precipitated by pouring into dilute sodium chloride solution. It is filtered ofi with suction and recrystallized from methanol. The dye dissolves readily in water and sensitizes a silver iodobromide emulsion with a maximum at 542 m (0.04 g. of dyestufi added to 1 kg. of emulsion).

Example 2 2.3 g. of 2-methyl-5-thienyl benzoxazole and 2 g. of p-toluene sulphonic acid ethyl ester are heated in an oil bath for 1 /2 hours at C. After working up with acetone, there are obtained 3 g. of 2-n1ethyl-3-ethyl-5- thienyl benzoxazoliumtosylate. This is boiled for about 3 minutes with 20 cc. of pyridine and 3 cc. of ethoxy acrolein aceta-l and added to dilute potassium bromide solution. The precipitate is filtered oil. with suction and recrystallised from methanol.

The absorption maximum of the dye is at 600 mg and the sensitisation maximum with a silver bromide emulsion at 630 mg ,0.005 g. of dyestuif per 1 kg. of emul sion).

12 g. of a quaternary salt of 2-methyl-5-thienyl benzoxazole and butanesultone as described in Example l are boiled for 3 hours with pyridine and orthopropionic ester (12 cc.). The resulting dye is precipitated by pouring the liquid into dilute sodium chloride solution, and is filtered oif with suction and recrystallised from a mixture of methanol and ethanol. The dye is filtered off with suction and washed with a mixture of ethanol and propanol. r The dye absorbs in alcohol at 510 m while in water the dye has an extremely intense absorption maximum at 570 mp, which can be clearly detected even in extremely dilute form and can serve for the recognition of minute traces of dye. The sensitisation maximum with a silveriodobromide emulsion is at 565-570 m with a steep drop towards the longer wavelengths. The dye can also be used for sensitizing color film emulsions which contain the usual color components.

Example 4 to form a strongly fluorescing solution with an adsorption maximum at 570 me. The dye has a broad sensitization 0 H: range in a silver iodobromide emulsion in which it is possible to detect two maxima at 550 and 590 mm (0.015 g. of S 6-0 dyestufli per 1 kg. of emulsion). T i The new dyes are suitable for sensitizing both black- N+ :35 and-white and color emulsions which contain dye components, since they are compatible with the dye components. They can be used alone or admixed with other 2 8- 0f y y OIe and 2 g. of ethyl 10 known dyes, and in individal cases hypersensitization eftoluenesulphonate are heated for about 1 /2 hours in an fa ts can ur, oil bath at 120 C. The resulting quaternary salt is washed with acetone and immediately further condensed. Example 7 The product is dissolved in 20 cc. of pyridine, and 1.7 g.

0 0 of 1-ethyl-2methyl-mercapto-6-methoxy-quinoline ethyl toluenesulphonate and 5 cc. of pyridine are added, where- S upon the mixture is boiled for 10 mintues and then poured S [l l r i l l 01115 C M into dilute potassium iodide. The solid which separates out can be recrystallised from ethanol. The dye has a sensitisation maximum at 505 m with a silverchlorobromide emulsion and the sensitization curve falls steeply to- 4.5 g. of Z-methyl-S-threnyl benzoxazole ethyl tosylate wards long'w-ave ralige (002.5 of iiyestuff per (see Example 2), 6 cc. of orthopropionic acid ethyl ester, of emulsion the silver salt of which consists of silver 8 cc of pyridine and 1 cc of acetic acid anhydride are bromide and 75% sllver chloride) heated to about 120 C. for 1 /2 hours. The reaction mix- I 5 25 ture is poured into dilute aqueous potassium bromide solu- Examp 6 tion and the precipitated dyestufi bromide is crystallized 0 S from methanol.

The sensitization maximum is at about 565 mp (0.05 g. s of dyestufi per 1 kg. of a silveriodobromide emulsion (5% W U O(l7-N 30 silveriodide, 95% silverbromide).

N B Example 8 o=on-on=0 1 o-oH=0H-oH=c S N r f l can 01H;

4.1 g. of 2-methyl-3-ethyl-5-thienyl-benzoxazole tosyl- 8.6 g. of 2-methyl-5-thienyl benzoxazole are heated with 15 g. of ethyl iodide on the water bath for some days. 5 g. of the quaternary salt of the following composition A are thus obtained ate as described in Example 2, 2.3 g. of 3-ethyl-5-ethoxy methylene rhodanene and 30 cc. of pyridine are heated in an oil bath for 40 minutes at 125 C. The resulting mixture is filtered while hot and the filtrate is left overnight in a refrigerator. The precipitate is filtered off with suction and recrystallised from a mixture of chloroform and i I It (113B;

methanol. Sensitization maximum with a silver bromide emulsion 560 mp (0.025 g. of dyestuff per 1 kg. of emul- 1- $1011) 5 g. of this compound are heated to the boil for 20 w mintues with 2.5 g. of diphenyl formamidine and 20 cc. of Example 6 acetic anhydride. The reaction mixture is treated with '2 g. of the dimethine merocyanine according to Example acetone. The following compound B (2.1 g.; M.P.: 5 are heated for a short time with'0.8 cc. of dimethyl sul- 217 C.) is obtained. phate at 120 C. The internal temperature of the mixture (B) 0 rises to 125 C. Thereafter, 12 cc. of pyridine and 2 g. of Zoom the 2-methyl-3-ethy1-5-thienyl benzoxazole tosylate de- S CCH=CHNCOHB scribed in Example 2 are added and the temperature is if T kept for 35 minutes at 120 C. By precipitation with dilute potassium bromide solution, the dye is isolated as an r amorphous powder, and for purification purposes is re- 0.85 g. of this compound and 0.75 g. of the compound crystallized twice from ethanol. It is dissolved in ethanol of the following composition which is described in the 10 V wherein R represents a member selected from the group consisting of lower alkyl and lower alkyl-substituted by sulfo groups; and

wherein the associated anion is a monovalent acid anion when R is lower alkyl, and wherein a betaine structure is formed when R isa sulfo-substituted lower alkyl; R stands for a lower alkyl radical, Z represents the atoms necessary to complete a heterocyclic ring selected from the group consisting of benzthiazolyl, naphthiazolyl, thiazolyl, 2-sulfo-4-keto-thiazolidinyl, benzselenazolyl, selenazolyl, benzoxozolyl, 5-a-thieny1-benzoxazolyl, naphthoxazolyl, oxazolyl, quinolyl, S-methoxy-quinolyl and methyltetrahydrobenzthiazolyl, and m and n are whole numbers from 0 to 2 inclusive.

2. A photographic silver halide emulsion optically sensitizedrwith an effective amount of a cyanine dye having the formula:

1/ 100 mol of the intermediate product -B of Example 8, 1/100 mol of the 2,6-dirnethyltetrahydrobenzthiazol-iodoethylate, 2.5 g. of sodium acetate and 50 cc. of acetic an- 3. A photographic silver halide emulsion optically sensitized with an effective amount of a cyanine dye having the formula:

CCH=CHCH=C s N 5,11. la.

4. The optically sensitized silver halide emulsion of claim 1 in which the cyanine dye is:

/ S Ill 5. The optically sensitized silver halide emulsion of claim 1 in which the cyanine dye is:

Ca s 2 11 12 6. The optically sensitized silver halide emulsion of 10. The optically sensitized silver halide emulsion of claim 1 in which the cyanine dye is: claim 1 in which the cyanine dye is:

so, son; H 7. The optically sensitized silver halide emulsion of claim 1 in which the cyanine dye is:

o OCHa References Cited in the file of this patent 15 UNITED STATES PATENTS N 1,969,445 Brooker Aug. 7, 1934 I I (EH5 5 2,060,383 Schneider Nov. 10, 1936 2,083,804 Zeh June 15, 1937 8. The optically sensitized silver halide emulsion of g g fi Z claim 1 in which the cyanine dye is: a e

0 2,403,723 Ka ser July 9, 1946 /5\ 2,461,137 Brooker Feb. 8, 1949 2471996 Anish May 31 1949 c cH-cH c cs 1 g 1 2,857,394 de Stevens Oct. 21, 1958 l N O 1 I 1 01H; OTHER REFERENCES 2 6 The optically sensitized silver halide emulsion f Chemical Abstracts, 16, 3101 (Abstract of Brit. Med. claim 1 in which the cyanine dye is: 1922, PY in J- 0 Chemical Abstracts, 19, 530 (Abstract of Proc. Roy

Soc., London, 96B, 317-33, 1924). (Copy in Sci. Libr.). S C-GH=CHCH=C s B l 1 T \N W J I z 1 EH appear as shown below instead of as in the patent:

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,044,875 July 17, 1962 Johannes Go'tze It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, lines 16 to 21, formula II should appear as shown below instead of as in the patent:

I NH column 3, lines 50 to 56, formula VIII should appear as shown below instead of as in the patent: 1

, 3" 1 column 4, line 145, strike out "Asymmetrical carbocyanines"; line 46, for :"are obtained read one obtains asymmetrical carbocyanines -5 same column 4, line 51, for "gutaconic-"i read glutaconic column 6 lines 49 to $6, the formula should 3- 3 column 7, line 45, for "rhodanene" read rhodanine Signed and sealed this 14th day of May 1963.

(SEAL) Attest:

DAVID L. LADD 

1. A PHOTOGRAPHIC SILVER HALIDE EMULSION OPTICALLY SENSITIZED WITH AN EFFECTIVE AMOUNT OF A CYANINE DYE CONTAINING A THIENYL-SUBSTITUTED BENZOXAZOLE RING AND BEING SELECTED FROM THESE HAVING THE FOLLOWING FORMULA: 